The S-Pol radar was developed at NCAR/ATD to replace the CP-2 radar which served the research community for nearly twenty years. The purpose of S-Pol is to provide a cost effective state-of-the-art polarimetric weather radar for world wide deployment.

S-Pol has several significant improvements compared with CP-2. Its container transportation method allows practical temporary deployments worldwide including remote and difficult geographic sites. Additionally, S-Pol uses a high performance modern transmitter, low sidelobe parabolic antenna with high isolation between horizontal and vertical channels, and a modern dual channel receiver. The NCAR-designed VME data system provides numerous computed variables.

S-Pol completed operational tests during the spring of 1996 and is available for routine field deployments through the usual NCAR/ATD channels.

The entire S-Pol radar including generators and operations control area is packaged into six 20 foot sea containers. These containers are of a standard size which can easily be handled in seaports. They also can be shipped overland or by air as necessary. Site preparation and restoration costs are minimized because the antenna support structure is made from the shipping containers themselves. Although typically a radome is not required, the existing CP-2 radome system could be used to enclose the entire radar in extreme environments. The pedestal will be able to sufficiently control the exposed antenna in a 50 MPH wind.

The transmitter is an ASR-9 based unit built by Westinghouse. It uses an air cooled klystron and produces a one megawatt, one microsecond pulse. The PRF can range from 325 to 1200 pulses per second. The transmit pulse is tapered and filtered for minimum RF interference. The 28 foot reflector is a high-compliance aluminum structure providing -30 dB first sidelobes and at least -35 dB integrated cross polar isolation.

Polarization switching will be done by an NCAR built mechanical switch which will provide 49 dB transmit isolation. For alternating H/V pulses, this isolation is comparable to a dual transmitter configuration. A separate receiver for each channel provides 40 dB receive isolation. Dual receivers are required for cross polar measurements and to enable the low channel dwell times of the mechanical switch.

Pulse pair and dual polarization processing is performed by a NCAR designed VME-based Integrated Radar Acquisition system (VIRAQ). The VIRAQ processor uses a dual range 90 dB digital IF system with multiple C44 DSP chips that are controlled by a 486 CPU host running DOS.

S-Band Polarization Radar (S-Pol) Characteristics

20 ft. containers

Site requirements

leveling and access


Diesel generator


2.7 -- 2.9 GHz

Pulse width

.3 -- 1.4 Ásec-tapered


0 -- 1300 Hz

Peak power


Staggered pulse


Random phase jitter for 2nd trip supression



Meets radio frequency management
Subsection 5.2.3, Criteria C

Receivers (2)

H & V simultaneously

Noise power

-115.5 dBm

Radar Noise figure

2.9 dB

Dynamic range

90 dB


.738 MHz

Digital IF

Linear floating point processing

I-Q image rejection

50 dB

Minimum detectable dBZ at 50km/1km

-15 dBZ/-52 dBZ at -6 dB SNR

Polarization switching

H-V alternating or H only

Mechanical switch isolation

47 dB measured

Ferrite switch isolation

28 dB


Parabolic, center feed


44.5 dB including wave guide loss


8.5 m (28 ft.)


0.91 degrees

First sidelobe

better than -30 dB

Isolation (ICPR)

better than -35 dB

Scan rate

Up to 18░/s each axis, 30░/s with pulley change

Wind limit for operation

30 m/s / 60 m/s (no radome)

Data system

NCAR designed VME system (VITAQ)

Number of range gates


Gate spacing

37.5 -- 1000m

Number of samples

16 -- 1000

Clutter filter

Single polarization only, 50 dB

Times series (I/Q) capability


Real time scientific display

NCAR Zebra

Recorded variables

PHH, PVV, V, W, R(1)HV, R(1)VH|, |R(2)|, PhiDP, PhoHV, NCP, ZH, ZDR, LDR, Kdp

Recording medium

Exabyte, Dorade format

For more information, contact Jon Lutz


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